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AGA/NAJA Calculator for OEC vs MRB

sledge

Ideal_Rock
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Apr 23, 2018
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4,381
It's been awhile since I looked for it, but tonight I was trying to find the AGA/NAJA calculator that used to be available here:


Not sure if the update @psadmin performed broke this link, or if @denverappraiser requested it be taken down as I also no longer see it on the datlas.com website either.

Would love some feedback.

Primary purpose was I found an older article linking an OEC against a MRB, and was wanting to make sure I understood properly.


FWIW, these are the stats of the GIA report on the MRB I am curious about:
  • 55 table
  • 36 crown angle
  • 16.5 crown height
  • 43 pavilion depth (40.8 pavilion angle)
  • medium to slightly thick girdle, 3.5%
  • excellent polish & symmetry
  • 63.3 total depth
If I have interpreted correctly, the MRB in question would hit the far left (excellent) side of the modern cut class 1-2 chart, indicating this MRB would rival a well cut OEC.

When I look at the Wiki section, using the GIA data above you can see how various elements falls across a few different planes but none are worse than a 2B stone.


This isn't a stone I would typically recommend, but the person inquiring has a unique set of circumstances and I believe this may be the better of two available stones.
 
Last edited:

Karl_K

Ideal_Rock
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Aug 4, 2008
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8,949
sloooow down lol
I think if Im reading it right you asked about a dozen questions.
The key to understanding oec cuts is in how they differ from mrb cuts.
 

Karl_K

Ideal_Rock
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8,949
  • 55 table
  • 36 crown angle
  • 16.5 crown height
  • 43 pavilion depth (40.8 pavilion angle)
  • medium to slightly thick girdle, 3.5%
  • excellent polish & symmetry
  • 63.3 total depth
GIA numbers are absolutely useless for this combo.
There is a huge difference in quality and appearance possible inside the gia rounding.
Off the top of my head from AGS 0-1 to ags5ish.
With the 3.5 girdle if LP was 0 it would likely trigger the spread penalty and get a 1 most likely as I remember.
 

Karl_K

Ideal_Rock
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Al's book I reference and I consider it a must read is available for free in pdf form:
 

Karl_K

Ideal_Rock
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AGA I have no clue what is up with it...
It was awesome in its day but has been surpassed by the hca and agsl ray tracing.
I have a ton of respect for Dave Atlas he is truely a modern pioneer in cut research as well as a great guy.
 

sledge

Ideal_Rock
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Apr 23, 2018
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FWIW, LGF's are reported at 75. Of course, no pics or video available.

My homebrew Excel calculator shows potential for considerable variation as you mention. This is based off the AGS proportions charts and don't take the minor facets, etc into consideration. Nor any rounding issues -- well kind of I guess, as I am going out in diameter to estimate where range could fall.


Capture.PNG
 

sledge

Ideal_Rock
Premium
Joined
Apr 23, 2018
Messages
4,381
AGA I have no clue what is up with it...
It was awesome in its day but has been surpassed by the hca and agsl ray tracing.
I have a ton of respect for Dave Atlas he is truely a modern pioneer in cut research as well as a great guy.
I have a feeling it was removed because of aging. I agree newer technology has came out that would supersede it. But big kudos for the brain power of providing some sort of technology at that point in time.

I guess what I found interesting was the link I posted earlier where he attempted to compare MRB to OEC performance. This caught my interest as I was hoping that even though this MRB in question doesn't have ideal proportions, it may offer beauty in a different way.

Thanks for the link to the book...I will have a read.
 

oldminer

Ideal_Rock
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Sep 3, 2000
Messages
6,345
The AGA/NAJA Cut Class Calculator is gone from view due to maturation of the trade’s approach to defining the quality of diamond cut. Also, there were software issues with the old programming that were no longer worth upgrading for display on Pricescope or on my own website.

When I created this set of parameters and then automated the rules to get consistent results, there was no one knew of openly supplying such unbiased advice to consumers. Thankfully, the lack of advice has led to much more meaningful information. It was time to put the AGA tool to rest.

What I found from creating the Cut Class tool was a long term friendship with Garry Holloway. At the same time in the 80’s and early 90’’s he was on a parallel course developing the HCA 12,000 miles away. The coincidence of our mutual thought processes was an amazing and rare event. It was an early, pre-internet preview of how sharing information can really change things.

I continue to support and encourage the open sharing of knowledge by all on Pricescope.
 

sledge

Ideal_Rock
Premium
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Apr 23, 2018
Messages
4,381
Thank you for the clarification David. You are a class act, sir.

I appreciate you, Garry and others who continue to push themselves and the industry for unbiased information to properly educate consumers.

I am sorry to see your product enter retirement but I am grateful for your knowledge and input here. More importantly that you gained a long term friendship with similar views and expertise that I am sure has allowed both you & Garry to help grow one another professionally over the years.

Lastly, my apologies with the wrong name call out in my initial post. I could see your face, but obviously failed to get the proper name tag of @oldminer input in my post.

Thank you again, I appreciate you taking the time to clarify.
 

OoohShiny

Ideal_Rock
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Apr 25, 2014
Messages
6,862
+1 to Sledge's comments! :))


  • 55 table
  • 36 crown angle
  • 16.5 crown height
  • 43 pavilion depth (40.8 pavilion angle)
  • medium to slightly thick girdle, 3.5%
  • excellent polish & symmetry
  • 63.3 total depth
GIA numbers are absolutely useless for this combo.
There is a huge difference in quality and appearance possible inside the gia rounding.
Off the top of my head from AGS 0-1 to ags5ish.
With the 3.5 girdle if LP was 0 it would likely trigger the spread penalty and get a 1 most likely as I remember.
FWIW, LGF's are reported at 75. Of course, no pics or video available.

My homebrew Excel calculator shows potential for considerable variation as you mention. This is based off the AGS proportions charts and don't take the minor facets, etc into consideration. Nor any rounding issues -- well kind of I guess, as I am going out in diameter to estimate where range could fall.


Capture.PNG
So this combo could potentially be awesome or potentially be a total dud? lol
 

headlight

Brilliant_Rock
Joined
Nov 2, 2003
Messages
1,853
Thank you for the clarification David. You are a class act, sir.

I appreciate you, Garry and others who continue to push themselves and the industry for unbiased information to properly educate consumers.

I am sorry to see your product enter retirement but I am grateful for your knowledge and input here. More importantly that you gained a long term friendship with similar views and expertise that I am sure has allowed both you & Garry to help grow one another professionally over the years.

Lastly, my apologies with the wrong name call out in my initial post. I could see your face, but obviously failed to get the proper name tag of @oldminer input in my post.

Thank you again, I appreciate you taking the time to clarify.
I would like to echo your sentiments @sledge regarding the contributions of @oldminer!
 
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